1. Field of the Invention
This invention relates to the use of a fatty oil ex Helianthus annuus for the preparation of emulsifiers for emulsion polymerization.
2. Statement of Related Art
It is known that alkali metal salts of fatty acids are particularly suitable for the emulsion polymerization of monomers, such as butadiene, styrene, chloroprene or acrylonitrile; cf. R. R. Dunbrook, India Rubber Wld. 117, 203 (1948). Stable latices are formed and may readily be coagulated by acidification or with a saturated sodium chloride solution. It has been shown that, compared with one another, the salts of C.sub.16 -C.sub.18 fatty acids used as emulsifiers in the copolymerization of butadiene give the same polymerization velocities of the monomers (H. Bartl , Houben-Weyl , Methoden der organischen Chemie, Vol. XIV/1, Makromolekulare Stoffe, Part 1, page 193, Georg-Thieme-Verlag, Stuttgart (1961). Unsaturated fatty acids are distinguished from saturated fatty acids having the same number of carbon atoms by their liquid consistency and by the better solubility of their alkali metal salts. This provides for better handling in practice. For example, sodium oleate has already played a significant role in the development of the emulsion polymerization of synthetic rubber. It is an effective emulsifier, even at low temperatures (M. H. Reich, B. Moss, J. M. Gyenge, Rubber Age (N.Y.) 76, page 391 (1954)). In addition, sodium and potassium oleate as polymerization emulsifiers are described in U.S. Pat. No. 2,469,132; U.S. Pat. No. 2,589,919; U.S. Pat. No. 2,418,782; German Patent 923,333; GB 744,455; and U.S. Pat. No. 2,623,032.
Although oleates are thus well known as polymerization emulsifiers, it has been found that polymerization is affected where the soaps contain relatively large proportions of polyunsaturated fatty acids. This is normally the case where the soaps are obtained from fats of natural origin, cf. C. W. Carr, I. M. Kolthoff, E. J. Meehan, R. J. Stenberg, J. Polymer Sci. 5, 191 (1950) and J. W. Wilson, E. S. Pfau, Ind. Eng. Chem. 40, 530 (1948). The polymerization reaction is inhibited particularly severely by sodium linoleate (J. W. Wilson, E. S. Pfau, loc. cit.). Sodium oleate has already been used as a regulator in the synthesis of rubber (H. Bartl, loc. cit., page 194; Germany Patent 706,548; and W. Graulich, W. Becker, Makromol. Chem. 3, 70 (1949)).
Accordingly, there has been no shortage of attempts to produce oleic acids of low linolenic and linoleic acid content which are suitable for polymerization purposes. Although it is possible relatively easily to convert tallow fatty acid into a fatty acid composition eminently suitable for the production of synthetic rubber by selective catalytic hydrogenation, the advantage of oleic acid in terms of handling, namely its liquid consistency, is lost in this hardening process.
In practice, liquid and solid fatty acids can be separated by
hydraulic pressing,
solvent separation, or
rolling-up by the Twitchell process (cf. H. Schoenfeld
(Ed.), Chemie und Technologie der Fette und Fettprodukte, Vol., 2, pages 534 et seq, Verlag Julius Springer, Vienna, 1937).
Although it should be possible to separate polyunsaturated fatty acids from oleic acid by extraction processes, the sulfur dioxide proposed as extractant for this purpose can only be handled with considerable safety precautions, cf. German patent 434,794. Modern processes for the recovery of oleic acid are based either on the separation of solid and liquid fatty acids by hydrophilization or by solvent extraction. It is only olive oil fatty acid that can be directly obtained without separation steps from the splitting of olive oil, but unfortunately the product composition of this fatty acid is highly variable. Normally, olive oil fatty acid still contains about 10 to 15% saturated fatty acids which adversely affect the particle size of the latex. Accordingly, olive oil is not normally suitable as an emulsifier for emulsion polymerization. In addition, fatty acids of high oleic acid content are available from the hoofs of slaughtered cattle (neat's-foot oil, 79% oleic acid), although in this case, too, separation with wetting agents or an extraction process is normally carried out to free the oleic acid from around 20% saturated fatty acids. Finally, tall oil has been used as a raw material for emulsifiers for emulsion polymerization. However, the abietic acid content of tall oil makes a catalytic hardening process (disproportionation) absolutely essential, cf. German patent 2,510,803.